In the production of polyurethane foams, use is frequently made of polyether-polysiloxane copolymers which can be divided into two classes of stabilizers. Polyether-polysiloxane copolymers in which the polyethers are linked via an SiOC bond to the polysiloxane chain have been known for a long time. Such copolymers are prepared by reacting hydroxyl-functional polyethers either with chlorosiloxanes in a substitution reaction or with alkoxysiloxanes in a transesterification reaction. This product group advantageously displays a wide processing latitude and a high activity, i.e., polyurethane foams which have a fine cell structure, the desired proportion of open/closed cells and are free of foam defects are obtained in a wide concentration range of the stabilizer. Owing to these properties, polyurethane (PU) stabilizers of the SiOC product group can be widely used in many formulations. A disadvantage is the limited hydrolysis stability of the SiOC bond which leads to the stabilizers and in particular their blends or formulations not being able to be stored for a long time. A further disadvantage of the SiOC stabilizers is their moderate solubility in polyol formulations, which can lead to turbidity or even to separation phenomena of the fully formulated polyol formulation. This problem occurs particularly in the case of rigid foam applications in which solubility and separation stability of preformulated mixtures of polyols, catalysts, water/blowing agents, the foam stabilizer and optionally further additives, which are marketed as ready-to-use polyurethane foam systems, are frequently required.
To counter the unsatisfactory storage stability, a second class of polyether-polysiloxane copolymers in which the polyethers are bound via hydrolysis-stable SiC bonds to the polysiloxane has been developed. These copolymers are prepared by noble metal-catalysed hydrosilylation of allyl polyethers by means of hydrogensiloxanes. PU stabilizers of the SiC product group display, in addition to their very good storage stability, a high solubility in polyol formulations. However, when used in high-resilience flexible foam applications, the broad processing latitude known for SiOC stabilizers is not obtained since the amount of stabilizer used has to be kept constant within a narrow range in order to achieve consistently good foam properties.